A Hubble Space Telescope image of Pluto and its moons. Charon is the largest moon close to Pluto. The other four bright dots are smaller moons discovered in 2005, 2011 and 2012.

Pluto's entire moon system is believed to have formed by a collision between the dwarf planet and another planet-sized body early in the history of the solar system. The smashup flung material that coalesced into the family of satellites observed around Pluto.

"The moons form a series of neatly nested orbits, a bit like Russian dolls," said team lead Mark Showalter of the SETI Institute in Mountain View, Calif.

The known moons of Pluto are:

Charon: Discovered in 1978, this small moon is almost half the size of Pluto. It is so big Pluto and Charon are sometimes referred to as a double planet system.

Nix and Hydra: These small moons were found in 2005 by a Hubble Space Telescope team studying the Pluto system.

Kerberos: Discovered in 2011, this tiny moon is located between the orbits of Nix and Hydra.

Styx: Discovered in 2012, this little moon was found by a team of scientists search for potential hazards to the New Horizons spacecraft flyby in 2015.

Scientists are searching for more possible moons orbiting Pluto and also signs of a possible debris field generated by the theoretical impact billions of years ago.